The invention relates to a method for detecting faults in an electronically controlled drive system of a motor vehicle and, in particular, to a method for detecting faults in an electronically controlled drive system of a motor vehicle by way of an electronic control unit which detects at least the accelerator pedal position and the longitudinal acceleration of the motor vehicle as input signals of the electronic control unit.
As a result of standards required by law (for example, ISO or CARB Standard Regulations), for many years, motor vehicle manufacturers have had to meet the requirement that electronic control units or electronically controlled systems in motor vehicles, such as the digital engine control or the adaptive transmission control, have to be capable of self-diagnosing. For example, the so-called OBD (On-Board Diagnosis) systems were developed on this basis. One example of a further development of an OBD system can be found in the applicant's German Patent document DE 197 31 283 A1.
In this respect, the electronic control units in the interior of the vehicle require a large amount of software for the purpose of self-diagnosis in addition to the software necessary for the purpose of actual functional control. One example of a self-diagnosis in the interior of the control device is described in the applicant's German Patent Document DE 196 12 857 A1.
Until now, the focus of the fault diagnosis required by law had been on the intrinsic safety of each individual control unit or each electronically controlled vehicle system itself. This results in high application expenditures. Particularly in the case of an engine control or internal-combustion engine control (for spark ignition engines or Diesel engines), a large number of stored characteristic diagrams will accumulate when each programmed function has to be secured. One example, just for the expenditures of a functional programming where a desired driving power is predefined as a function of the accelerator pedal position, is described in the applicant's German Patent Application DE 102 49 689 A1. If the characteristic diagrams for the functional programming illustrated there were to be diagnosed in an intrinsically secure manner, approximately twice the programming expenditures or twice the storage space would be required. The reason is that a fault detection threshold would have to be stored for each characteristic curve of the characteristic diagrams (for the principle, see FIG. 8).
In this case, “αFP” is the position of the accelerator pedal, and “MA” is the desired drive torque. The characteristic curve illustrated in FIG. 8 (as a solid line) is one of many desired characteristic curves for which (shown by a broken line) a characteristic fault detection curve would be programmed.
It is an object of the invention to simplify a method for detecting faults in a drive system of a motor vehicle.
This and other objects are achieved according to the invention by a method for detecting faults in an electronically controlled drive system of a motor vehicle by way of an electronic control unit which detects at least the accelerator pedal position and the longitudinal acceleration of the motor vehicle as input signals of the electronic control unit. Independently of its actual functional scope, a first fault detection program is carried out by the control unit, by which a fault is detected when a defined acceleration gradient, dependent on an accelerator pedal position change, is exceeded for longer than a predefined time period.
In the case of the method according to the invention for detecting faults in an electronically controlled drive system of a motor vehicle by way of an electronic control unit, the electronic control unit collects at least the accelerator pedal position and the longitudinal acceleration of the motor vehicle as input signals. Independently of its actual functional scope, a first fault detection program can be carried out by the control unit, by which a fault is detected when a defined acceleration gradient dependent on an accelerator pedal position change is exceeded for longer than a predefined time period. The control unit is correspondingly programmed for implementing the method according to the invention.
The defined acceleration gradient, that is dependent on a change of the accelerator pedal position, preferably is limited by the maximal slope of a characteristic curve of the actual functional scope, by which a desired vehicle acceleration is predefined as a function of the accelerator pedal position. This maximal slope is determined empirically, particularly in driving tests, in order to detect which acceleration gradients the driver can still be expected to handle or control. The defined acceleration gradient(s) that is/are dependent on an accelerator pedal position change is/are stored in a memory of the control unit and integrated in the program of the control unit for implementing the method according to the invention.
In a further development of the invention, when the accelerator pedal is not actuated, a second fault detection program can be implemented by the control unit independently of its actual functional scope, by which second fault detection program, a fault is detected when a defined acceleration threshold value—which preferably is dependent on the vehicle speed—is exceeded longer than for a predefined time period.
In a further embodiment of the invention, in the event that a wheel slip control system is not activated, a third fault detection program can be implemented by the control unit independently of its actual functional scope, by which third fault detection program, a fault will be detected when, while the accelerator pedal is not actuated or the accelerator pedal angle is decreasing, an acceleration gradient determined from the rotational wheel speeds is positive longer than for a predefined time period, and simultaneously, a vehicle acceleration gradient not determined from the rotational wheel speeds is also positive. For this purpose, the control unit receives either directly or by way of digital bus information the rotational wheel speed values or the acceleration determined from the rotational wheel speeds as an input signal or signals. The rotational wheel speeds are detected anyhow in a known manner, for example, for a slip control, by way of corresponding sensors. A vehicle acceleration gradient not determined from the rotational wheel speeds may be determined, for example, by means of its own longitudinal acceleration sensor or from the speedometer signal (for example, the rotational transmission output speed).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.